Magnetic recording media comprising a non-magnetic support having provided thereon a magnetic layer containing ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, CrO.sub.2, or ferromagnetic alloy particles dispersed in a binder have conventionally been used as video tapes, audio tapes, magnetic disks and the like.
In recent years, demands for higher density recording has been realized and recording wavelengths have been shortened. Thus, spacing loss upon recording and reproducing (i.e., outputs are decreased due to a thick magnetic layer) has become a serious problem.
In view of the above, the thickness of a magnetic layer has been reduced. However, if a magnetic layer has a thickness of about 2 .mu.m or less, the surface of the magnetic layer is readily affected by the surface properties of the support, thereby deteriorating electromagnetic properties.
A thick non-magnetic underlayer is provided on a support and a magnetic layer is thereafter provided thereon as an upper layer to prevent the magnetic layer from being affected by the surface roughness of the support. However, head wear-out property and durability in this case are not satisfactory and further improvements are necessary.
The above-described conventional non-magnetic underlayer uses thermosetting (hardenable type) resins as a binder. Therefore, since the underlayer is hardened, the magnetic layer contacts with a magnetic head or other equipment parts without buffer conditions, and the magnetic recording medium having such a hardened underlayer has rather poor plasticity.
In order to avoid the above problems, it has been proposed that non-hardenable (thermoplastic) resins be used in the underlayer. However, when a magnetic layer is provided as an upper layer after such an underlayer is provided and dried, the underlayer is swollen by the organic solvents contained in the coating solution for the upper layer which causes disturbance in the coating solution used for the upper layer, thereby deteriorating surface properties of the magnetic layer and decreasing the electromagnetic properties. Accordingly, it has been believed that the underlayer should not use a nonhardenable binder.